Efficient removal of anti-inflammatory from solution by Fe-containing activated carbon: Adsorption kinetics,...

This work developed an innovative activated carbon (ICAC) derived from orange peels (OP) through chemical activation using FeCl₃. The traditional activated carbon (PCAC) that was prepared through K₂CO₃ activation served as a comparison. Three adsorbents (ICAC, PCAC, and OP) were characterized by various techniques, these being: Brunauer-Emmett-Teller (BET) surface area analysis, thermo-gravimetric analysis, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. They were applied to remove diclofenac from aqueous solution applying batch experiments, in order to investigate the characteristics of adsorptive kinetics, isotherms, and thermodynamics. Results indicated that the S_BET values were in the following order: 457 m²/g (PCAC) > 184 m²/g (ICAC) > 3.56 m²/g (OP). The adsorption process reached a fast equilibrium, with activating energies being 27.6 kJ/mol (ICAC), 16.0 kJ/mol (OP), and 11.2 kJ/mol (PCAC). The Langmuir adsorption capacities at 30 °C exhibited the decreasing order: 144 mg/g (ICAC) > 6.44 mg/g (OP) > 5.61 mg/g (PCAC). The thermodynamic parameters demonstrated a signal dissimilarity between biosorbent (ΔG° <0, ΔH° <0, and ΔS° <0) and activated carbon samples (ΔG° <0, ΔH° >0, and ΔS° >0). The presence of iron (FeOCl, γ-Fe₂O₃, and FeOOH) on the surface of ICAC played a determining role in efficiently removing diclofenac from solution. The excellent adsorption capacity of ICAC toward diclofenac resulted presumably from the contribution of complicated adsorption mechanisms, such as hydrogen bonding, ion-dipole interaction, π-π interaction, pore filling, and possible Fenton-like degradation. Therefore, FeCl₃ can serve as a promising activating agent for AC preparation with excellent efficiency in removing diclofenac.